Electric locking devices such as electric strikes, for example, are typically used as components in electronic locking systems to provide security access control in buildings or the like. They are fitted to a door jamb, usually in association with a mechanical lock. The strike includes a pivotally moveable keeper which retains the door latch of the mechanical lock. When the strike is in an unlocked condition, the keeper is free to rotate and release the door latch of the mechanical lock so the door may be pushed open. When the strike is in a locked condition, the keeper is not free to rotate and the door can only be opened by withdrawing the door latch manually.
The strike can be controlled by way of a card reader, or another access control system, located on the outside of the door. Typically, no handle is provided on the outside of the door, and a rotatable handle is provided on the inside of the door. Therefore, from the inside, persons may operate the handle to leave the building or area. From the outside, persons may only enter if they activate the access control system to release the electric strike from its locked condition.
Electric locking devices such as electric strikes are often subjected to a condition known as “pre-load”. Pre-load is the name given to lateral forces applied to the keeper. These lateral forces may be caused, for example, by warpage of a door or door frame, a person pushing on the door, or differences in air pressure on either side of the door such as might be caused by air conditioning or building ventilation systems.
If an electric strike is subjected to pre-load, this can affect correct operation of the strike. For instance, when under pre-load, the mechanism of the strike may become jammed and be unable to transition from a locked condition to an unlocked condition. As well as being unsatisfactory and inconvenient, this situation also raises serious safety concerns. In the event of an emergency or the like, a central control system may send a signal to the strike to adopt the unlocked condition. If the lock becomes jammed due to pre-load, then there is a risk that persons may be trapped behind doors, or that emergency workers cannot gain access through doors from the outside.
There remains a need to provide for electric locking devices with improved pre-load capabilities.